The present disclosure is related to a projection zoom lens and a projection type display device. The present disclosure is related to a projection zoom lens which is suited to magnify and project original images which are formed by light valves onto a screen, for example, and a projection type display device equipped with such a projection zoom lens.
Conventionally, projection type display devices that utilize light valves, such as liquid crystal display elements, DMD's (Digital Micromirror Devices: registered trademark), etc., are in wide use. Particularly, projection type display devices of configurations that employ three light valves, each corresponding to illuminating light beams of the three primary colors, R (red), G (green), and B (blue), combine light beams which are modulated by each of the light valves with a prism or the like, and display images on screens via a projection lens, are in wide use.
It is necessary for projection lenses which are utilized in projection type display devices to have a focusing function, because the distance from the projection type display devices to screens and screen sizes vary according to installation environments. The inner focus method, in which a lens most toward the magnification side does not move, is known as a focusing method that is employed in projection lenses. In addition, there is a tendency for zoom lens systems having a magnification changing function to be preferred as projection lenses, so as to be capable of adjusting the sizes of projected images according to screen sizes in various installation environments. Japanese Unexamined Patent Publication No. 2001-066501, Japanese Patent No. 5253604, and Japanese Unexamined Patent Publication No. 2011-013657, for example, disclose conventionally known zoom lenses that employ the inner focus method.
Japanese Unexamined Patent Publication No. 2001-066501 discloses a zoom lens, in which a first lens group provided most toward the object side is constituted by a first lens group front group having a positive refractive power and a first lens group rear group having a negative refractive power, and only the first lens group rear group moves during focusing operations. Japanese Patent No. 5253604 discloses a zoom lens, in which a first lens unit provided most toward the magnification side is constituted by, in order from the magnification side to the reduction side, a 1A lens sub unit having a negative optical power and a 1B lens sub unit having a positive optical power, and the 1A lens sub unit is fixed while the 1B lens sub unit moves during focusing operations. Japanese Unexamined Patent Publication No. 2011-013657 discloses a projection zoom lens, in which a second lens group, which is a lens group provided second from the magnification side, moves during focusing operations.